An automatic sprinkler system is one of the most widely used devices for fire protection. These systems have sprinklers that are activated once the ambient temperature in an environment, such as a room or a building, exceeds a predetermined value. Once activated, the sprinklers distribute fire-extinguishing fluid, preferably water, in the room or building. A sprinkler system, depending on its specified configuration is considered effective if it controls or suppresses a fire. Failures of such systems may occur when the system has been rendered inoperative during building alteration or disuse, or the occupancy hazard has been increased beyond initial system capability.
The sprinkler system can be provided with a water supply (e.g., a reservoir or a municipal water supply). Such supply may be separate from that used by a fire department. Regardless of the type of supply, the sprinkler system is provided with a main that enters the building to supply a riser. Connected at the riser are valves, meters, and, preferably, an alarm to sound when water flow within the system exceeds a predetermined minimum. At the top of a vertical riser, a horizontally disposed array of pipes extends throughout the fire compartment in the building. Other risers may feed distribution networks to systems in adjacent fire compartments. Compartmentalization can divide a large building horizontally, on a single floor, and vertically, floor to floor. Thus, several sprinkler systems may serve one building.
In a piping distribution network, branch lines carry the sprinklers. A sprinkler may extend up from a branch line, placing the sprinkler relatively close to the ceiling, or a sprinkler can be pendent below the branch line. For use with concealed piping, a flush-mounted pendant sprinkler may extend only slightly below the ceiling.
The sprinkler system can be provided in various configurations. In a wet-pipe system, used for example, in buildings having heated spaces for piping branch lines, all the system pipes contain a fire-fighting fluid, such as, water for immediate release through any sprinkler that is activated. In a dry-pipe system, used for example, in unheated open areas, cold rooms, passageways, or other areas exposed to freezing, such as unheated buildings in freezing climates or for cold-storage rooms, the pipes, risers, and feed mains, disposed, branch lines and other distribution pipes of the fire protection system may contain a dry gas (air or nitrogen or mixtures thereof) under pressure. A valve is sued to separate the pipes that contain a dry gas and pipes that contain a fire-fighting fluid, such as, water. In some application, the pressure of gas holds closed a dry pipe valve at the riser. When heat from a fire activates a sprinkler, the gas escapes and the dry-pipe valve trips; water enters branch lines; and fire fighting begins as the sprinkler distributes the water. By its nature, a dry sprinkler system is slower to respond to fire conditions than a wet system because the dry gas must first be exhausted from the system before the fire-fighting fluid is expelled from the fire sprinkler. Such delay creates a “water delivery time” to the sprinkler. The water delivery time introduces an additional variable for consideration in a design for fire protection with a dry pipe system.
Various standards exist for the design and installation of a fire protection system. In particular, the National Fire Protection Association (“NFPA”) describes, in its Standard for the Installation of Sprinkler Systems 13 (2002) (“the NFPA Standard 13”) various design consideration and installation parameters for a fire protection system, which standard is incorporated herein by reference in its entirety. One of many design considerations provided by NFPA Standard 13 is the number of fire sprinklers to be used in a fire protection system. For a wet system, the NFPA Standard 13 describes at A.14.4.4 that a quantity of fire sprinklers can be determined either by a design area calculation or by a specified minimum number of sprinklers.
NFPA Standard 13 also addresses certain design considerations for dry pipe fire protection systems by modifying the design of the wet pipe system. For example, in a dry pipe system, NFPA Standard 13 states, for commercial storage (NFPA Standard 13, 12.1.6.1) and dry pipe system generally (NFPA Standard 13, 14.4.4.4.2), that a design area for a dry pipe system is to be increased 30% over the design area for the wet system in such applications so that the quantity of fire sprinklers for a dry pipe system is increased by generally 30% over the same quantity of fire sprinklers in a wet system. Where Large-Drop Sprinklers are utilized in commercial fire protection, NFPA shows (at Table 12.3.2.2.1(b) and 12.3.4.2.1) that an increased in the specified number of sprinklers is (e.g., 50% or more) is required when a dry pipe system is utilized instead of a wet pipe for these sprinklers. When a commercial fire sprinkler is used with a dry pipe instead of a wet pipe system in dwelling applications, the design area must be increased by 30% so that the number of these sprinklers must be increased, and thus, the hydraulic demand is increased. It is apparent from NFPA Standard 13 that, holding all other design parameters constant, the use of a dry pipe system instead of a wet pipe system would require a relatively large increase in the number of fire sprinklers, which would increase the hydraulic demand of the dry pipe system.
Although NFPA Standard 13 refers in broad terms to wet pipe and dry pipe systems, NFPA Standard 13 is generally silent as to design and installation criteria for dry pipe residential sprinkler systems. For example, NFPA Standard 13 fails to specify any criteria in a design of a dry pipe residential fire sprinkler system, including a hydraulic demand calculation, the quantity of residential fire sprinklers consonant with the hydraulic demand calculation or installation constraints and use of residential fire sprinklers in a dry pipe fire protection system. In fact, NFPA Standard 13 (2002) specifically prohibits residential fire sprinklers from being used in any system other than wet unless the residential fire sprinklers are listed for such other applications, as stated in NFPA Standard 13 at 8.4.5.2:                [R]esidential sprinklers shall be used only in wet systems unless specifically listed for use in dry pipe systems or preaction systems. (Emphasis Added).        
NFPA provides separate standards for design and installation of wet pipe fire protection system in residential occupancies. Starting in 1975, NFPA provides the Standard for the Installation of Sprinkler Systems in One-And Two-Family Dwellings and Manufactured Homes 13D (“NFPA Standard 13D”). Due in part to the increasingly urbanized nature of cities, NFPA promulgated, in 1989, another standard in recognition of low-rise residential facilities, entitled Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to And Including Four Stories in Height 13R (“NFPA Standard 13R”). The latest respective editions of NFPA Standard 13D and 13R are the 2002 Edition of NFPA Standard 13 and 13R, which are incorporated by reference herein in their entirety. Starting in 1988, Underwriters Laboratory (“UL”) provides for additional requirements that residential fire sprinklers must meet for residential fire protection systems as set forth in its Underwriter's Laboratory Residential fire sprinklers for Fire-Protection Service 1626 (“UL Standard 1626”). The most recent edition of UL Standard 1626 is the October 2003 edition, which is incorporated by reference herein in its entirety.
NFPA and UL provide similar water density requirement for residential fire protection systems. NFPA Standard 13 (2002) states (Chap 11.2.3.5.2) that a density for a protection area of a residential occupancy with a generally flat ceiling as the greater of (a) 0.1 gallons per minute per square feet of the four most hydraulically demanding sprinkler over a design area or (b) a listed residential minimum density. The listed residential minimum density can be found in either NFPA Standard 13D or 13R (2020). NFPA Standard 13D (2002) states (Chapter 8.1.1.2.2 and 8.1.2) that fire sprinklers listed for residential use shall have minimum discharge density of 0.05 gallons per minute per square feet to the design sprinklers, where the number of design sprinklers includes all of the sprinklers, up to a maximum of two, that requires the greatest hydraulic demand, within a compartment that has generally flat and smooth ceiling. NFPA Standard 13R (2002) states (Chapter 6.7.1.1.2.2. and 6.7.1.2) that fire sprinklers listed for residential use shall have minimum discharge density of 0.05 gallons per minute per square feet to the design sprinklers, where the number of design sprinklers includes all of the sprinklers, up to a maximum of four, that requires the greatest hydraulic demand, within a compartment that has generally flat and smooth ceiling. UL Standard 1626 (October 2003), on the other hand, states (at Table 6.1) that the density for a coverage area with a generally flat ceiling as 0.05 gallons per minute per square feet minimum.
Although NFPA Standards 13R and 13D provide considerable flexibility in the design and installation of wet pipe residential fire protection system, these standards are strict in prohibiting any existing residential fire sprinklers that are approved for use in a wet pipe residential system from being used in any application other than a wet system. In particular, both NFPA Standard 13R and 13D (2002) reiterate the stricture stated NFPA Standard 13 (2002), which prohibits the use of residential sprinklers for systems other than wet pipe by stating, at paragraphs 6.6.7.1.2 and 7.5.2, respectively, that:                [R]esidential sprinklers shall not be used on systems other than wet pipe systems unless specifically listed for use on that particular type of system. (Emphasis Added).        
While these standards may have considered a residential piping system other than a wet pipe system, e.g., a dry pipe residential system, the standards do not provide any indication of how to determine a hydraulic demand as part of a design of such systems. Furthermore, because of the guidelines in the standards regarding the use of dry pipe instead of wet pipe, those desiring to use a dry pipe sprinkler system in non-residential applications would normally increase the hydraulic demand of the dry pipe system over that of the wet pipe system, either by an increase in the design area or the number of sprinklers based on the wet pipe system. Currently, it is believed that no residential fire sprinkler is approved for a dry pipe system in residential applications. Thus, design methodologies and installation requirements for applications other than wet pipe fire sprinkler systems in residential applications are believed to be notably lacking.